British PM Theresa May on Friday said that London train bomb intended to cause 'significant harm'.

An improvised explosive device set off a small fire on a rush-hour train at a London subway station injuring at least 18 people Friday, none seriously, in an incident that British officials and police called a terrorist attack.

The incident happened shortly after 8 a.m. local time, when London's Underground system is crowded with commuters and children going to school. Most of the injuries were flash burns, London's Metropolitan Police said.

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